1. Field of the Invention
The present invention relates to a magnetic field application apparatus for initially magnetizing a medium onto which information is transferred and/or for reversing magnetization thereof. The present invention also relates to a magnetic transfer apparatus which includes the magnetic field application apparatus. The present invention also relates to a method for producing a magnetic recording medium.
2. Description of the Related Art
As a technique for producing a magnetic recording medium, a magnetic transfer technique is well known. According to the magnetic transfer technique, information corresponding to uneven patterns formed on a surface of an original disk (master information carrier) for transfer is magnetically transferred onto a medium (slave medium). Generally, in magnetic transfer, the medium onto which information is transferred is initially magnetized in a specific track direction. Then, the medium onto which information is transferred and the master information carrier are placed in close contact with each other, and a magnetic field in a direction opposite to that of the initial magnetization is applied. Accordingly, magnetization of the medium onto which information is transferred is reversed based on the uneven patterns on the surface of the original disk for transfer. Consequently, signal patterns are transferred onto the medium onto which information is transferred.
A magnetic field application apparatus for initially magnetizing a medium onto which information is transferred and/or for reversing magnetization thereof is disclosed in Japanese Unexamined Patent Publication No. 2003-272143 or the like.
A schematic diagram of the magnetic field application apparatus according to the related art is illustrated in FIG. 7A (a side view in a track direction). In FIG. 7A, the magnetic field application apparatus according to the related art includes a magnetic field application means 110 which has a pair of magnets 111 and 112, of which the polarities on the side facing a magnetic field application target 120 are different from each other. The direction of a magnetic field generated from one of the magnets toward the other magnet is a desired direction Hx. If the magnetic field application means 110 is placed on one side of the magnetic field application target 120, an unnecessary magnetic field in a perpendicular direction is applied to the magnetic field application target 120. The unnecessary magnetic field is a magnetic field in a direction other than the track direction (horizontal direction). Therefore, there is a possibility that the unnecessary magnetic field affects the accuracy of magnetic transfer. Therefore, the magnetic field application means 110 is provided on either side of the magnetic field application target 120, as illustrated in FIG. 7A.
In the magnetic field application apparatus illustrated in FIG. 7A, the magnetic field application target 120 is rotated relative to the magnetic field application means 110. Accordingly, the magnetic field in the desired direction Hx can be applied to the entire surface of the magnetic field application target 120.
In the magnetic field application apparatus illustrated in FIG. 7A, a magnetic field indicated with an arrow is generated. Therefore, the intensity of a magnetic field in a horizontal direction, applied to the magnetic field application target 120, is distributed, as schematically illustrated in FIG. 7B. In FIG. 7B, the horizontal axis shows the position of the magnetic field application target 120, corresponding to FIG. 7A, with respect to the horizontal direction, and the vertical axis shows the intensity of the magnetic field. In the vertical axis, the intensity of the magnetic field in the desired direction Hx is represented by positive (+) values. Here, the magnetic field in the perpendicular direction is cancelled out by the pair of magnetic field application means 110. Therefore, the magnetic field in the perpendicular direction is not applied to the magnetic field application target 120.
In the magnetic field application apparatus, magnetic fields in various directions are generated from the magnetic field application means 110. Therefore, a magnetic field in a direction HNG opposite to the desired direction Hx is applied to the magnetic field application target 120 at positions before and after the magnetic field application means 110 (immediately before the magnetic field application target 120 enters a position between the pair of magnetic field application means 110 and immediately after the magnetic field application target 120 moves out therefrom). In recent years, as the capacity of a magnetic field recording medium has increased, the intensity of a magnetic field applied to the magnetic field application target 120 has become higher. Therefore, an influence of the magnetic field in the opposite direction HNG on magnetic transfer has become substantial.